State Changes in .NET Implementation GS1 - 12 in .NET State Changes

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State Changes using visual studio .net todeploy upca with web,windows application barcode 39 Most modern OSs pro upc a for .NET vide some sort of signaling mechanism for inter-thread communication. One or more threads wait for a specific type of signal, which typically indicates a change in state.

On receiving the signal, the threads can process the changed state.. Under .NET, the wai t mechanism is encapsulated in a base class, WaitHandle, that provides methods to set a signal or wait for one or more signals. .

NET classes that are based on WaitHandle include AutoResetEvent,. ManualResetEvent, a upc barcodes for .NET nd Mutex. These classes wrap the corresponding synchronization handle provided by the.

OS. Events Under .N ET, events come in two varieties: AutoResetEvent and ManualResetEvent.

Both types of events, once signaled, remain signaled until a wait request is satisfied. In the case of AutoResetEvent, the state is automatically set to nonsignaled once a wait request is satisfied. In case of ManualResetEvent, the state remains signaled until Reset is called explicitly.

The following code excerpt implements a producer consumer mechanism using a Queue object and an. AutoResetEvent obje VS .NET UPC A ct. The producer adds items to the queue.

Each time it adds an item, it sends a signal to the. consumer thread. On receiving the signal, the consumer thread processes items from the queue. // Project StateCha .net vs 2010 UPC A nges/Events class MyQueue { private Queue m_Queue = new Queue(); private AutoResetEvent m_NewData = new AutoResetEvent(false); // producer public void AddData(int value) { lock(m_Queue.SyncRoot) { m_Queue.

Enqueue(value); } m_NewData.Set(); // signal } // dedicated consumer thread public void ConsumerThread() { while(m_NewData.WaitOne()) { lock(m_Queue.

SyncRoot) { while(m_Queue.Count > 0) { int value = (int) m_Queue.Dequeue(); Console.

WriteLine(value); } } } } }. The constructor for the AutoResetEvent takes a boolean parameter to indicate the initial state of the signal. A value of false implies that the state will remain nonsignaled initially..

The producer adds d UPC Symbol for .NET ata to the queue and signals the consumer thread by calling Set on the event object. The consumer thread waits for the event by calling WaitOne on the event object.

This method, which actually is defined on WaitHandle, blocks indefinitely until a signal is received. Upon receiving the signal, the consumer thread processes the data from the queue. Note that event signaling and protecting data from concurrent access are two different concepts (although used in conjunction most of the time).

As the queue is being shared between multiple threads, each thread still needs to lock the queue before accessing it. Besides WaitOne, WaitHandle provides many other forms of waits. For example, it is possible to wait for one signal from a group of signals using the static method WaitAny or to wait for all the signals from the group using another static method, WaitAll.

It is also possible to specify a wait timeout using both these methods. Finally, WaitHandle objects internally store synchronization handles from the OS. These handles are limited in number and should not be held if not needed.

To let you dispose of handles, WaitHandle implements. IDisposable. Althou gh not shown in the sample code, you should always implement IDisposable on a class. that contains an IDisposable-based field such as AutoResetEvent. Monitor Signals WaitHandle objects represent Windows OS waitable objects. Hence, they are not portable on other platforms..

However, the framew .net vs 2010 UPC A ork provides a portable version of event signaling via Monitor, a class that we have already used earlier for protecting shared objects. Using Monitor, our previous sample can be rewritten as follows:.

// Project StateCha nges/UsingMonitor class MyQueue { private Queue m_Queue = new Queue(); public void AddData(int value) { lock(m_Queue.SyncRoot) { m_Queue.Enqueue(value); Monitor.

Pulse(m_Queue); } } public void ConsumerThread() { lock(m_Queue.SyncRoot) { while(Monitor.Wait(m_Queue)) { while(m_Queue.

Count > 0) { int value = (int) m_Queue.Dequeue(); Console.WriteLine(value); } } }.

Static method Monit VS .NET UPCA or.Pulse is used to raise a signal for the specified object.

Static method Monitor.Wait is used to wait for a signal on the specified object. The object must be locked before either of these two methods can be called.

Looking at the code, the consumer thread locks the queue in the beginning and never seems to release it. You may be wondering how the method AddData ever gets to lock the queue. Actually method Monitor.

Wait is implemented such that it temporarily releases the lock and waits to reacquire the lock. This gives other threads a chance to lock the object and update the data. When Monitor.

Pulse is called, it causes the waiting thread to move to the active queue so that it can relock the object as soon as the other thread unlocks it.. Monitor has been im plemented as a purely managed class, that is, it is not tied to any native synchronization. primitives. This ma VS .NET UPC-A Supplement 2 kes it fully portable.

Also, it is more efficient in terms of OS resource requirements. So when does using WaitHandle-based objects make sense Here are two good cases: 1. 2.

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